Intermediate RF amplifiers between low power devices & PA's

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G8LES
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Joined: Wed Jul 23, 2008 11:28 am

Intermediate RF amplifiers between low power devices & PA's

Post by G8LES » Tue Dec 28, 2021 6:24 pm

Hello

There appears to be an unsolved issue now getting enough power to drive a PA unit for UK repeater outputs which are 1308 to 1318 MHz range.

Unfortunately the internal printed circuit layout on the Mitsubishi RAH modules has been modified and they only work at the low frequency end of 23 cms.

That of course produced a nice neat 3 stage FET amplifier solution, but even there they needed modifying for 1316/18 to shorten some of the track loops on the board otherwise after 1300 MHz the output power dropped rapidly.

What is needed is a 10 watt CW peak amplifier that will produce 2-5 watts of clean digital to drive a power amplifier.

Ideally also it should be able to work with Portsdown or Lime SDR's etc where the output power is low (1-10mW).

There are a lot of internally matched cellular phone transistors but it has to be a broadband device or it won't work.

I use the NXP MMG2024HT1 mimic's 17dB gain and 3 of those in cascade from a DATV Express transmitter drive for example a 2.4GHz 8watt Wi-Fi amp which in turn drives the Spectrian amplifier for QO100.

I can use the same mimic's for 23cm but it needs the output transistor.

I spotted the M509070N transistors on eBay, but they look a bit too much power.

The MRF284S 30watts CW looks more the type of device, it is broadband, and is 26 volts but the PA probably needs 26 volts anyway.

As it has 9dB of gain we need a clean 600mWatts to drive it, as a pre-driver then we can use our mimics.

Has anyone done a board for this purpose? Is anyone prepared to make one?

Regards

Mike G8LES

radiogareth
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Joined: Wed Jan 06, 2016 9:46 am

Re: Intermediate RF amplifiers between low power devices & PA's

Post by radiogareth » Wed Dec 29, 2021 9:05 am

Mike, I seem to recall that there is a 900MHz cell phone module that with minor changes works well on 23.
https://www.pa0p.com/apps/photos/photo? ... =205357740
Possibly just what you need...??
I bought a pair of the modules (yet to try) from AliExpress.
Gareth

radiogareth
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Joined: Wed Jan 06, 2016 9:46 am

Re: Intermediate RF amplifiers between low power devices & PA's

Post by radiogareth » Wed Dec 29, 2021 9:08 am

I should add (from Jim G7NTG) "take the cover off , remove the cap to ground on the track between stages and fit a 3pF ceramic trimmer between the output and ground. drill a hole in the lid to allow adjustment.
Jim
On 18 May 2021 at 19:03 James Smith <thebigclunk@virginmedia.com> wrote:
Hi Gareth
MHL9838 with mods will do it
https://www.pa0p.com/apps/photos/photo? ... =205357740
it's in Dutch
careful where you buy the chips from because the fakes will not modify
I have used lots of them for about 8W output

Hope that helps :-)

Gareth

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keng8vdp
Posts: 143
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Re: Intermediate RF amplifiers between low power devices & PA's

Post by keng8vdp » Fri Jun 30, 2023 6:14 pm

Hi. Raising this past thread again.

I have 2 x MHL9838 modules.
Could anyone confirm the following please.

There's a link to PA0P conversion info.
Google translate reveals the text in English
Under the photo.
On my modules there's already a capacitor across the
Output. Text under photo says
"Add a capacitor of 1-2pf at the output"
In my mind, add means leave the one that's already there" in which case the added capacitor of 1-2pf would be soldered in parallel with the one already there.
Now , looking at the photo I can't really tell if the original
One is still there / removed/ or new capacitor is piggy backed on top.

Can anyone clarify this please ?
Photo link : https://www.pa0p.com/apps/photos/photo? ... =205357740

Next question.
Powering / using the module.
Looking at the module . Pdf I see both stages powered at
30v ( I'm gonna use 28v)
Pins:
Pin 1/ RF input
Pins 2 & 3 / + volts
Pin 4/ RF out
Ground via module backplate & it's screws

Do I have the above correct ?
Also. There's no bias pin as on similar modules.
So I take it you simply power it up & it should go ?

I see Jim G7NTG suggests a trim pot instead of a fixed capacitor as shown in photo on link
https://www.pa0p.com/apps/photos/photo? ... =205357740

All advice is much appreciated

Many thank Ken

SkyVision
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Joined: Fri Jan 24, 2020 1:51 pm

Re: Intermediate RF amplifiers between low power devices & PA's

Post by SkyVision » Mon Jul 03, 2023 12:10 pm

Hi Ken

The SHL7008 is 24V, looks pretty much similar except there is 2 gate bias regulators, eBay item number:193754802490
The only mod is moving the cap, in yours it's removed and change out the existing cap to 1-2pf (lower) value
I scrapped the green mask back and moved the 4.7pf cap to the right to achieve best output power
Adjusting the output cap on mine didn't do much, they had 29-32db gain @ 1287mhz

Two modules and couple of Anaren hybrids beefed it up a bit, this also massages in and output match to 50ohms
I gave the dual unit to a guy in VK3 and to my knowledge he is still driving it with a pluto to get into the Melbourne repeater
The response is fairly wide band on these devices, the output match on a single unit looks good on mine (after the mod)
Out of around 7 devices, there were 2 sus ones, I may have mucked up, or the quality was poor, I can be impetuous and careless

It's not a substitue for the Mitshubishi Module, but thought it was ok for around a watt or so on DVB-S or as a driver
Tried driving Jim G7NTG's amp with one to get the power up, but it's still on the bench unfinished
No doubt someone smarter than me can take it to the next level

Cheers Roger VK5YYY
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keng8vdp
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Re: Intermediate RF amplifiers between low power devices & PA's

Post by keng8vdp » Mon Jul 03, 2023 12:37 pm

Hi Colin,

I tried copy paste the eBay number into eBay. Returns Item not found.

Re the mods, thanks for information, all noted.
I already have several working amplifiers.
All used on datv. I just happened to find 2 Motorola
Modules in a box of bits I rummaged through.
Fancied trying one.


Best regards. Ken

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